This invention relates to the preparation and use of aqueous dispersions or solutions of isocyanate polyaddition products and to adhesive films formed from such products. The invention more particularly relates to amine-terminated, polyurethane oligomers containing hydrophilic groups which are self-dispersing or soluble in water and which when combined with water-soluble or dispersed epoxy resins or blocked isocyanates react to form high molecular weight or cross-linked compositions.
Aqueous dispersions or solutions of isocyanate polyaddition products have been known in the prior art (see, e.g. U.S. Pat. No. 4,240,942 to Wenzel et al.). Such compositions have been known which have an average molecular weight of less than about 15,000, which contain from about 0 to 120 milliequivalents, per 100 grams of solid content, of built-in ionic groups or from about 0 to 25 percent by weight based on total weight of the oligourethane of built-in ethylene oxide units and which further contain primary or secondary aminic amino end groups or semicarbazide end groups containing at least one ##STR2## group. In addition, it is known that such oligourethanes can be reacted in aqueous phase with a chain-lengthening agent which is at least difunctional and which undergoes an addition reaction or condensation reaction with the amino end groups or semicarbazide end groups to effect chain lengthening of the oligourethanes.
It has further been known that polyurethanes, particularly solvent-based polyurethanes, could be used as adhesive compositions.
However, in the prior art it was not known how aqueous dispersions or solutions of oligourethanes, as previously described, could be used to form high quality adhesive films or layers. This was true because it was not recognized that prereaction in the aqueous system, as described in the prior art, destroyed adhesive qualities. In addition, such adhesive layers or films themselves were not previously known.
The formation of such layers or films from water dispersible or water-soluble oligourethanes is highly desirable to avoid solvent systems which are costly, often present a fire hazard and create pollution problems.